Conventionally, as for a curved tube applied to the bending portion of the piping forming the flow path for a fluid, for example, there are Patent Documents 1 and 2. In the Patent Document 1, a water-supply-pipe-insertion stopper protrusion inside an inner peripheral face of a bent portion is improved in an R shape so as to have a structure with little pressure loss (head loss). Also, in the Patent Document 2, when a main core of an inner die is pulled out to move, a swing member retracts and swings to an inward retraction position from a formation position by an undercut portion, and the swing member retracts and slides to the inward retraction position from the formation position by the undercut portion. Then, the swing member retracts and swings, and a sliding member retracts and slides, so that the main core can be pulled out of the curved tube.